The present invention relates generally to input of data to a computer system and, in particular, to a method and apparatus for improving the appearance of digitally represented handwriting input to such computer systems.
Portable computing platforms are a continually evolving component of computing technology. Increasingly, users of such systems are demanding levels of functionality in portable computing platforms equivalent to that found in more conventional desktop platforms. Technology currently exists to provide, in a portable platform, the functionality to which users have become accustomed in their more conventional platforms. One type of portable platform in this category is the so-called tablet computer.
Generally, tablet computers comprise a display screen and a digitizer co-extant with or integrated into the display screen. In combination with a stylus or other pen-like device, the digitizer is capable of capturing, as digital samples, movements of the stylus relative to the digitizer. The captured movements may then be displayed on the display screen, typically in real time. Using the stylus and digitizer combination, a user is able to xe2x80x9cwritexe2x80x9d on the computer""s display screen and have his or her handwriting captured and displayed on the display screen. The term xe2x80x9cinkingxe2x80x9d is sometimes used to distinguish this mode of data entry from other modes, e.g., typing on a keyboard or recognition of handwritten input. The capture and display of handwriting is considered a subclass of inking, which may otherwise include capturing freehand drawings and the like. Once captured, it is also known to perform character recognition analysis on the digital handwriting, thereby providing a convenient method of data entry.
The manner in which handwriting is digitized is illustrated in FIG. 4. As shown, various samples of the curves forming the handwriting are taken at periodic intervals. Typically, the samples comprise rectangular coordinates. Assuming a constant sampling period, the spacing between samples is indicative of the speed of the pen or stylus used to create the samples. The samples illustrated in FIG. 4 may be used to create a so-called polyline representation of the captured handwriting. In general, a polyline curve comprises a plurality of points with straight lines connecting successive points and, as such, represents an approximation of the actual curve. Higher sampling rates will generally provide a more accurate approximation. Stated another way, polyline curves introduce a level of noise or distortion to the curves they represent, which noise or distortion is a function, in part, of the sampling rate used and the speed at which the pen is moved. For example, using a typical sampling rate of 80 samples per second, handwriting displayed as polyline curves can be noticeably distorted. This problem is further exacerbated by the variability in human handwriting; some users have neat handwriting and others do not. Further still, sampling noise inherent in digitizers leads to additional inaccuracies in the resulting samples.
One technique used to improve the appearance of digitized handwriting is disclosed in U.S. Pat. No. 5,473,742 issued to Polyakov et al. and entitled Method And Apparatus For Representing Image Data Using Polynomial Approximation Method And Iterative Transformation-Reparameterization Technique (hereinafter xe2x80x9cPolyakovxe2x80x9d), the teachings of which patent are hereby incorporated by this reference. In general, Polyakov teaches a technique wherein polyline curves, particularly those representative of digitized handwriting, are converted to a parametric representation that reduces the distortions resulting from the factors described above. The results of the Polyakov technique, as applied to the digitized handwriting of FIG. 4, are illustrated in FIG. 5. As shown, the polyline representation of FIG. 4 is converted to a series of connected, parametric curves (twelve shown, separated by dots). As can be seen in FIG. 5, the resulting curves effect a smoothing of the original digitized handwriting, thereby improving overall appearance of the handwriting.
While the technique taught by Polyakov is helpful, it does little to address aliasing problems that can result when the smoothed handwriting is subsequently displayed on a display device. As known in the art, display devices can have varying resolution as determined by the number and geometry of the display elements (e.g., pixels) used to form the overall display area. In general, display devices have a lower resolution than digitizers of the type described above. The lower resolution provided by displays can lead to the aliasing effect. An example of this effect is illustrated in FIG. 6. FIG. 6 illustrates a highly magnified view of a grid of display elements 602 forming but a portion of a larger display area. A curve to be displayed is represented by the area between the two heavy lines having reference numerals 606a and 606b. Assuming that the foreground color (i.e., the color of the curve defined by the space between the heavy lines 606a-b) is different from the background color (i.e., the color of all areas outside the space defined by the heavy lines 606a-b), a dilemma is presented with regard to picture elements 608 that are not totally covered by the curve. That is, because the picture element 608 is the most basic display increment available and cannot be subdivided further, a decision must be made to activate the partially covered pixel 608 in accordance with the foreground color or the background color. If the foreground color is used, the curve will appear overly-thick and jagged. In contrast, if the background color is used, the curve will appear overly-thin and similarly jagged. The overall effect of aliasing is to decrease the perceived quality of appearance of the displayed curve. Because aliasing is a function of the display resolution, Polyakov and other similar techniques will not eliminate the effect of aliasing.
It would therefore be advantageous to provide a technique whereby the appearance of digital handwriting may be improved. Such techniques should preferably build upon existing techniques while simultaneously overcoming their limitations.
The present invention provides a technique whereby the appearance of digital handwriting may be improved. Digitized handwriting is captured and provided in real-time to a display in the form of polylines. The polylines are then converted to a parametric representation to effectively filter out the noise and distortion effects attributable to the process of obtaining digitized handwriting. To further refine quality, the filtered, digitized handwriting is subjected to edge-smoothing processing to mitigate the effects of relatively low-resolution displays. In this manner, the present invention improves the appearance of digitized handwriting in comparison to prior art techniques.